Multilayer glass ceramic substrate and process for producing the same

ABSTRACT

A multilayer glass ceramic substrate having a plurality of conductor layers each laminated through a glass ceramic layer. The glass ceramic layer has a composition comprising of alumina, borosilicate magnesium glass and cordierite crystal produced by chemical reaction between alumina and borosilicate magnesium glass. The content of alumina is 12 to 59.6 wt %, the content of borosilicate magnesium glass is 18 to 69.6 wt %, the content of the cordierite crystal is 1 to 50 wt % and the sum of components is 100 wt %. The multilayer glass ceramic substrate shows improved mechanical strength.

This application is a continuation of application Ser. No. 08,513,668,filed Aug. 4, 1995, now abandoned which was a continuation of Ser. No.08,073,725 filed Jun. 8, 1993 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multilayer glass ceramic substrateused for high density implementation of LSI elements and morespecifically to a multilayer glass ceramic substrate which can besintered at low temperatures and to a process for producing the same.

2. Description of the Related Arts

Development of semiconductor technology require down-sizing andhigh-speed of electronics devices and systems. In fact, as thesemiconductor elements are integrated into VLSI and ULSI of highdensity, very high density and fine-processing ale required in theimplementation technique for assembling the elements. In particular, itis requested to increase the wiring density of the substrate on whichsemiconductor elements are implemented so as to comply with finerpattering and higher operation speed and to lower the dielectricconstant of substrate materials.

Alumina multilayer substrate has been used widely. This substrate isproduced by a thick film printed multilayer technique or a green sheetlamination technique. The latter technique is more advantageous so as tosatisfy requirement of high-density integration. In the green sheetlamination technique, a plurality of thin ceramic green sheets each onwhich wiring lines are printed are laminated before integrated, so thatit is easy to increase the wiring layers to a desired number and hencethe wiring density can be increased comparing to the thick film printedmultilayer technique.

Alumina ceramic, however, has such a demerit that sintering must becarried out above 1,500° C. which require to use, as wiring conductor,Mo, W metal having a relatively high electric resistance and hence it isdifficult to realize fine wiring. Still more, the dielectric constant ofalumina is about 10 which is too high for high-speed operation ofsignals.

Recently, ceramic materials which can be sintered at relatively lowertemperatures have been developed so that low resistance conductors suchas Au, Ag--Pd, Ag or Cu can be used. For example, a composite materialconsisting of alumina and borosilicate lead glass can be sintered at alow temperature below 1,000° C. to produce a multilayer substrate inwhich Au, Ag--Pd or Ag can be used as a wiring conductor. However, inthis composite material, it is difficult to use wiring of Cu which is abase metal because the composite material contains lead and hencesintering can not be carried out in a reduction atmosphere. Still more,the electric constant of this composite material can not be loweredbelow 7.5.

Glass ceramic material using borosilicate glass is also know. This glassceramic material can be sintered at a temperature lower than 1,000° C.in a reduction atmosphere and has lower dielectric constant of about5.5, so that a multilayered structure having wiring lines of Cu can berealized simultaneously at the sintering of glass ceramic. Known glassceramic material, however, possess very poor mechanical strength becauseno crystallization occur by the sintering.

The mechanical strength is a very important factor of the substrate. Infact, in the case of a multi-chip implementation substrate on which alarge number of semiconductor elements are implemented, the substratesize increases and input/output terminals or pins are connected atdifferent levels, if the he mechanical strength of the substrate ispoor, problems of breakage of the substrate, junction failure or thelike occur in assembly stage and on a product.

An object of the present invention is to resolve the problems ofconventional implementation substrate and to provide a multilayer glassceramic substrate which can be sintered at a low temperature below1,000° C. in neutral and reduction atmosphere in addition to oxidationatmosphere and which has a low dielectric constant and improvedmechanical strength.

The multilayer glass ceramic substrate according to the presentinvention can be used as an implementation substrate for high-densityfine-wiring and high speed, since low resistance metals such as Au, Ag,Cu, Ag--Pd or the like can be used as wiring conductor.

SUMMARY OF THE INVENTION

The present invention provides a multilayer glass ceramic substratehaving a plurality of conductor layers each laminated through a glassceramic layer, characterized in that the glass ceramic layer has acomposition comprising of alumuina, borosilicate magnesium glass andcordierite crystal produced by chemical reaction between alumina andborosilicate magnesium glass, the content of alumina being 12 to 59.6 wt%, the content of borosilicate magnesium glass being 18 to 69.6 wt % andthe content of the cordierite crystal being 1 to 50 wt %, the sum ofcomponents being 100 wt %.

The composition can contain a forth component selected from a groupconsisting of silica glass, α-quartz and mullite. The content of theforth component is 10 to 30 wt %, the sum of components being 100 wt %.

The present invention provides also a process for producing a multilayerglass ceramic substrate by the steps of mixing material powders,preparing green sheets from slurry of the mixed material powders,forming via halls in the green sheets, printing wiring conductors on thegreen sheets and filling the via halls with conductor, laminating aplurality printed sheets, compressing the laminated sheets under heatand then sintering compressed sheets at a temperature below 1,000° C.,characterized in that the mixed material powders consists of 30 to 60 wt% of alumina powder and 70 to 40 wt % of borosilicate magnesium glasspowder.

In the process according to the present invention, cordierite crystalsare produce when alumina powder and borosilicate magnesium glass powderare sintered.

Alumina powder has preferably the average particle size of 0.5 to 3 μmand borosilicate magnesium glass powder has preferably the averageparticle size of 1 to 5 μm.

In a variation of the process according to the present invention, athird powder selected from a group consisting of silica glass, α-quartzand mullite is added to the material powders in such proportions as 10to 50 wt % of alumina powder, 40 to 70 wt % of borosilicate magnesiumglass powder and 10 to 50 wt % of the third powder, the sum of allpowders being 100 wt %.

The third powder has preferably the average particle size of 0.5 to 10μm.

The content of magnesium in the borosilicite magnesium glass ispreferably more than 5 wt % in term of magnesium oxide.

In the process according to the present invention, the material powdersor green sheets are sintered below 1,000° C. to produce a multilayerglass ceramic substrate having improved properties because of followingreason. In the sintering, borosilicate magnesium glass start to besoftened at about 700° C. The resulting liquidized glass penetrate intoand fill in spaces or clearances among ceramic powders of alumina, amongceramic powders of alumina and cordierite crystals and among ceramicpowders of alumina, cordierite crystals and quart glass, α-quartz ormullite to produce packed structure and a completely compacted glassceramic body is formed finally at a temperature range form 800° to1,000° C.

The material powders or green sheets of the present invention can besintered in a reduction atmosphere because the material powders of thepresent invention do not contain such elements that is reduced toelemental metal from oxide under the sintering condition. To thecontrary, in the case of known material powders containing for examplelead oxide, lead oxide is converted, in the reduction atmosphere, tometal lead which seriously deteriorate the insulation property of theresulting glass ceramic body obtained.

The multilayer glass ceramic substrate according to the presentinvention possesses improved mechanical strength which is one of veryimportant properties required in implementation of semiconductorelements. Usually, the bending strength of higher than 2,000 kg/cm² isrequired in the substrate for implementing semiconductor elements. Themultilayer glass ceramic substrate according to the present inventionsatisfies this strength because a compacted fine structure is realizedby the sintering. In fact, the reaction between alumuina and liquidizedglass produces the cordierite crystal, so that the resulting glassceramic obtained by the sintering possess a fine strong structure inwhich particles of alumina, particles of cordierite crystal (and alsoparticles of silica glass, α-quartz or mullite, if they exist) andglassy mass are bonded three-dimensionially and which has all improvedbending strength.

In the process according to the present invention, sintering can beeffected below 1,000° C., the multilayer structure can be easilyrealized by the green sheet lamination technique and any conductorincluding basic metals such as Cu, Ni, their alloys or those that mustbe sintered in neutral or reduction atmosphere in addition to noblemetals of Au, Ag, Pd, Pt or the like can be used.

The multilayer glass ceramic substrate according to the presentinvention possesses improved mechanical strength or bending strength ofhigher than 2,000 kg/cm² and low, dielectric constant and makes itpossible to realize fine wiring with high implementation density.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Now, Examples of the present invention is explained but the presentinvention is not limited to the Examples.

EXAMPLE 1

(Alumina+borosilicate magnesium glass)

As material powders alumina powder and borosilicate magnesium glasspowder were used.

Alumina powder having the average particle size of 0.5 μm to 3 μm andborosilicate magnesium glass powder having the average particle size of1 to 5 μm were intimately mixed at a proportion range from 30 wt % 70 wt% to 60 wt %:40 wt %.

Borosilicate magnesium glass used have following composition by weight:

    ______________________________________                                        B.sub.2 O.sub.5                                                                       15             CaO    1                                               SiO.sub.2                                                                             65             BaO    1                                               MgO     12             TiO.sub.2                                                                            1                                               Na.sub.2 O                                                                            2              ZrO.sub.2                                                                            1                                               K.sub.2 O                                                                             2                                                                     ______________________________________                                    

The resulting mixed material powder was dispersed together with anorganic binder of polyvinyl butyral, polyvinyl alcohol or polyacrylicresin in a solvent to prepare a slurry from which a green sheet wasmolded by slip casting technique. The thickness of the green sheet wasadjusted in a range from 10 to 400 μm.

Then, via halls connecting upper and lower conductors were formed in thegreen sheet bit a punching machine. A wiring pattern was printed byscreen printing technique with conductor past and the via halls werefilled with the conductor past. The conductor past used consisted mainlyof Au, Ag, Ag--Pd, Cu, Ni or Ag--Pt.

Predetermined numbers of green sleets each on which the conductorpattern was printed and of which the via hall was filled were laminatedand compacted under heat. Then, the laminated green sheets were heatedto a temperature of 400° to 700° C. to remove the organic binder and thesolvent (elimination of bindery).

Finally, the laminated green sheets were sintered at a temperatureranging form 800° to 1,000° C. to obtain a multilayer glass ceramicsubstrate. During this sintering stage, the cordierite crystal isproduced by a chemical reaction between alumina and borosilicatemagnesium glass and the softened glass mass penetrate into and fillspaces or clearances among particles so as to promote compactedstructure.

Composition of glass ceramic layer of sintered substrates obtained aresummarized in Table 1. The composition bias determined bar usual X-raydiffraction method. The contents of alumina and cordierite crystal whichare determined by comparing their peaks to a peak of silicon used as areference and a proportion of borosilicate magnesium glass is calculatedby subtracting their contents from the total.

Conductor, sintering conditions, numbers of layers and wiringspecification used for manufacturing multilayer glass ceramic substratesas well as the results obtained are summarized in Tables 2 and 3. Thesample numbers in Table 1 correspond to those in Tables 2 and 3.

                  TABLE 1                                                         ______________________________________                                        Alumina + borosilicate magnesium glass                                               Composition ratio (wt %)                                               Sample                Borosilicate                                                                            Cordierite                                    Number   Alumina      glass     crystal                                       ______________________________________                                        1        12           38        50                                            2        12           43        45                                            3        12           48        40                                            4        17.4         32.6      50                                            5        18.1         37.6      44.3                                          6        18.2         50.1      31.7                                          7        22.0         29.1      48.9                                          8        23.2         39.5      37.3                                          9        23.3         48.7      28.0                                          10       23.5         57.3      19.2                                          11       27.9         29.8      42.3                                          12       28.1         41.0      30.9                                          13       28.1         50.5      21.4                                          14       28.3         61.8      9.9                                           15       33.2         18.9      47.8                                          16       33.3         31.6      35.1                                          17       33.3         35.3      31.4                                          18       33.5         46.9      19.6                                          19       38.4         27.7      33.9                                          20       38.4         31.4      30.2                                          21       38.7         34.7      26.6                                          22       38.8         50.7      10.5                                          23       42.0         18.0      40                                            24       42.1         33.8      24.1                                          25       42.1         37.3      20.6                                          26       42.3         43.2      14.5                                          27       46.3         38.2      15.5                                          28       46.3         43.7      10.0                                          29       48.4         18.0      33.6                                          30       48.6         20.9      30.5                                          31       48.7         29.8      21.5                                          32       48.7         35.2      16.1                                          33       52.5         21.8      25.7                                          34       52.5         27.4      20.1                                          35       52.6         30.3      17.1                                          36       52.8         34.1      13.1                                          37       56.1         29.8      14.1                                          38       56.3         33.7      10                                            39       56.3         38.5      5.2                                           40       56.5         42.5      1.0                                           ______________________________________                                    

                                      TABLE 2                                     __________________________________________________________________________                          Number                                                                             Size of Wire       Coefficient                          Sintering        of   Wire Wire                                                                              Via  Specific                                                                           of Thermal                                                                          Breaking                                                                           Insulation           Sample                                                                             Temperature                                                                              Sintering                                                                           Layers                                                                             Width                                                                              Pitch                                                                             Diameter                                                                           Inductive                                                                          Expansion                                                                           Strength                                                                           Resistance           No   (°C.)                                                                        Conductor                                                                          Atmosphere                                                                          (Layer)                                                                            (μm)                                                                            (μm)                                                                           (μm)                                                                            Capacity                                                                           (×10.sup.-7 deg.sup.-1                                                  )     (kg/cm.sup.2)                                                                      (Ω -           __________________________________________________________________________                                                             cm)                   1   900   Ag   Air   30   120  300 150  5.4  40    2200 >10.sup.13            2   900   Ag   Air   30   120  300 150  5.3  41    2300 >10.sup.13            3   910   Ag--Pd                                                                             Air   30   120  300 150  5.2  43    2300 >10.sup.13            4   880   Cu   N.sub.2                                                                             30   120  250 120  5.5  40    2200 >10.sup.13            5   850   Cu   N.sub.2                                                                             30   120  250 120  5.5  43    2300 >10.sup.13            6   850   Cu   N.sub.2                                                                             30   120  250 120  5.1  46    2600 >10.sup.13            7   900   Cu   N.sub.2 + H.sub.2                                                                   40   150  300 150  5.8  40    2300 >10.sup.13            8   910   Cu   N.sub.2 + H.sub.2                                                                   40   150  300 150  5.6  44    2300 >10.sup.13            9   900   Ag   Air   40   150  300 150  5.3  48    2400 >10.sup.13           10   900   Ag   Air   40   150  300 150  5.0  49    2600 >10.sup.13           11   890   Ag   Air   40   150  300 200  5.8  43    2700 >10.sup.13           12   880   Ag   Air   40   150  300 200  5.6  47    2500 >10.sup.13           13   900   Ag--Pd                                                                             Air   40   150  300 200  5.5  49    2400 >10.sup.13           14   880   Ag--Pd                                                                             Air   30   150  300 200  5.2  52    2600 >10.sup.13           15   880   Ag--Pd                                                                             Air   30   100  200 100  6.5  41    2600 >10.sup.13           16   900   Ag--Pd                                                                             Air   30   100  200 100  6.2  45    2400 >10.sup.13           17   870   Ag   Air   30   100  250 120  6.2  46    2500 >10.sup.13           18   850   Ag   Air   30   100  250 120  6.0  49    2500 >10.sup.13           19   890   Ag   Air   30   100  250 120  6.2  47    2700 >10.sup.13           20   900   Ag   Air   35   100  300 150  6.1  47    2500 >10.sup.13           __________________________________________________________________________

                                      TABLE 3                                     __________________________________________________________________________                          Number                                                                             Size of Wire       Coefficient                          Sintering        of   Wire Wire                                                                              Via  Specific                                                                           of Thermal                                                                          Breaking                                                                           Insulation           Sample                                                                             Temperature                                                                              Sintering                                                                           Layers                                                                             Width                                                                              Pitch                                                                             Diameter                                                                           Inductive                                                                          Expansion                                                                           Strength                                                                           Resistance           No   (°C.)                                                                        Conductor                                                                          Atmosphere                                                                          (Layer)                                                                            (μm)                                                                            (μm)                                                                           (μm)                                                                            Capacity                                                                           (×10.sup.-7 deg.sup.-1                                                  )     (kg/cm.sup.2)                                                                      (Ω -           __________________________________________________________________________                                                             cm)                  21   900   Cu   N.sub.2                                                                             35   100  300 150  6.1  43    2500 >10.sup.13           22   850   Cu   N.sub.2                                                                             35   100  300 150  5.8  48    2800 >10.sup.13           23   930   Cu   N.sub.2                                                                             35   100  300 150  6.8  39    2400 >10.sup.13           24   900   Cu   N.sub.2                                                                             40   150  300 150  6.1  45    2500 >10.sup.13           25   910   Cu   N.sub.2 + H.sub.2                                                                   40   150  350 150  5.9  48    2500 >10.sup.13           26   900   Au   Air   40   150  350 150  5.8  50    2600 >10.sup.13           27   900   Ag   Air   40   150  250 150  5.8  51    2700 >10.sup.13           28   880   Cu   N.sub.2                                                                             40   150  250 150  6.2  53    2800 >10.sup.13           29   950   Cu   N.sub.2                                                                             40   120  300 120  6.7  45    2500 >10.sup.13           30   930   Ag--Pd                                                                             Air   30   120  300 120  6.6  47    2500 >10.sup.13           31   900   Ag--Pd                                                                             Air   30   120  300 120  6.4  49    2400 >10.sup.13           32   900   Au   Air   30   120  300 120  6.2  51    2300 >10.sup.13           33   930   Cu   N.sub.2                                                                             30   120  250 100  6.7  48    2400 >10.sup.13           34   910   Cu   N.sub.2                                                                             30   120  250 100  6.5  50    2400 >10.sup.13           35   950   Ag--Pd                                                                             Air   30   120  250 100  6.4  51    2300 >10.sup.13           36   950   Ag--Pd                                                                             Air   30   100  200  80  6.4  51    2300 >10.sup.13           37   930   Ag--Pd                                                                             Air   40   100  250 120  6.7  50    2400 >10.sup.13           38   960   Ag--Pd                                                                             Air   40   100  250 120  6.5  52    2300 >10.sup.13           39   900   Ag   Air   40   100  250 120  6.4  54    2200 >10.sup.13           40   900   Cu   N.sub.2                                                                             40    80  200  80  6.5  55    2100 >10.sup.13           __________________________________________________________________________                                                             1                

Tables 2 and 3 reveal such facts that multilayer glass ceramicsubstrates having the compositions according to the present inventionshown in Table 1 posses improved properties required in practical usesincluding satisfactory mechanical strength and that fine wiring ofhigh-density can made easily.

On the contrary, when the content of alumina is less than 12 wt %, thebending strength of substrate become lower than 2,000 kg/cm² and isinsufficient. If the alumina content exceed 59.6 wt %, sintering can notbe carried out below 1,000° C. so that the insulation resistancedecrease and that the bending strength become lower than 2,000 kg/cm²and the dielectric constant becomes higher than 7, which isdisadvantageous for high-speed circuits. In these cases, practicalmultilayer glass ceramic substrate can not be produced.

When the content of borosilicate magnesium glass is not higher than 18wt %, it is impossible to obtain a glass phase sufficient to fill spacesor clearances among alumina particles, so that the strength become lowerand the reliability can not be expected. It the content of borosilicatemagnesium glass exceed 69.6 wt %, the strength intrinsic to classdominates so that the bending strength become less than 2,000 kg/cm².

If the content of the cordierite crystal is less then 1 wt %, the effectfor reinforcing the strength obtained by the presence of cordieritecrystals can not be expected so that it is impossible to obtain thebending strength of more than 2,000 kg/cm². If the content of thecordierite crystal exceed 50 wt %, the multilayer glass ceramicsubstrate does not shrink uniformly and hence the reliability is lost.

If the content of magnesium in the borosilicate magnesium glass used asa material powder becomes less than 5 wt % in term of magnesium oxide,no or little cordierite crystal is produced by sintering, operation.

If the particle size of alumina powder used becomes lower than 0.5 μm orhigher than 3 μm, and if the particle size of borosilicate magnesiumglass powder become lower than 1 μm or higher than 5 μm, the mixedmaterial powder can not be sintered satisfactorily, so that theresulting multilayer glass ceramic substrate shows very poor reliabilityand hence can not be used in practical uses.

EXAMPLE 2

(Alumina+borosilicate magnesium glass+silica glass)

Example 1 is repeated except silica glass was added to the materialpowders of alumina powder and borosilicate magnesium glass powder.

Namely, alumina powder having the average particle size of 0.5 μm to 3μm, borosilicate magnesium glass powder having the average particle sizeof 1 to 5 μm and silica glass powder having the average particle size of0.5 μm to 10 μm were intimately mixed at a proportion of (alumina+silicaglass):borosilicate magnesium glass of front 30 wt %:70 wt % to 60 wt%:40 wt %. The proportion of alumina powder was adjusted above 10 wt %.

Composition of glass ceramic layer of sintered substrates obtained aresummarized in Table 4 and conductor, sintering conditions, numbers oflayers and wiring specification used for manufacturing multilayer glassceramic substrates as well as the results obtained are summarized inTables 5 and 6. The sample numbers in Table 4 correspond to those inTables 5 and 6.

                  TABLE 4                                                         ______________________________________                                        Alumina + borosilicate magnesium glass + silica glass                         Composition ratio (wt %)                                                      Sample                      Borosilicate type                                                                       Cordierite                              Number Alumina  Silica glass                                                                              Glass     crystal                                 ______________________________________                                        101    12.0     21.0        37.0      30.0                                    102    12.0     30.0        33.0      25.0                                    103    12.4     11.0        69.6      20.0                                    104    17.0     25.0        32.0      26.0                                    105    17.0     10.0        23.0      50.0                                    106    18.0     21.0        40.0      21.0                                    107    22.0     18.0        25.0      35.0                                    108    23.0     15.0        27.0      35.0                                    109    23.0     19.0        38.0      20.0                                    110    23.0     24.0        20.0      33.0                                    111    28.0     20.0        19.0      33.0                                    112    28.0     11.0        51.0      10.0                                    113    28.0     17.0        40.0      15.0                                    114    28.0     17.0        35.0      20.0                                    115    33.0     17.0        36.0      14.0                                    116    33.0     12.0        25.0      30.0                                    117    33.0     18.0        20.0      29.0                                    118    34.0     10.0        45.0      11.0                                    119    38.0     19.0        18.0      25.0                                    120    38.0     24.0        24.0      14.0                                    121    39.0     15.0        28.0      18.0                                    122    39.0     11.0        40.0      10.0                                    123    42.0     11.0        18.0      29.0                                    124    42.0     12.0        28.0      18.0                                    125    42.0     10.0        30.0      18.0                                    126    42.5     13.0        34.5      10.0                                    127    46.0     10.0        31.0      23.0                                    128    46.0     11.0        33.0      10.0                                    129    48.0     11.0        18.0      23.0                                    130    48.0     12.0        21.0      19.0                                    131    49.0     10.0        21.0      20.0                                    132    49.0     15.0        26.0      10.0                                    133    52.0     12.0        18.0      18.0                                    134    52.0     12.0        20.0      16.0                                    135    53.0     11.0        22.0      14.0                                    136    53.0     11.0        24.0      12.0                                    137    56.0     10.0        25.0      9.0                                     138    56.0     10.0        21.0      13.0                                    139    57.0     10.0        24.0      9.0                                     140    59.6     10.0        19.4      11.0                                    ______________________________________                                    

                                      TABLE 5                                     __________________________________________________________________________                          Number                                                                             Size of Wire       Coefficient                          Sintering        of   Wire Wire                                                                              Via  Specific                                                                           of Thermal                                                                          Breaking                                                                           Insulation           Sample                                                                             Temperature                                                                              Sintering                                                                           Layers                                                                             Width                                                                              Pitch                                                                             Diameter                                                                           Inductive                                                                          Expansion                                                                           Strength                                                                           Resistance           No   (°C.)                                                                        Conductor                                                                          Atmosphere                                                                          (Layer)                                                                            (μm)                                                                            (μm)                                                                           (μm)                                                                            Capacity                                                                           (×10.sup.-7 deg.sup.-1                                                  )     (kg/cm.sup.2)                                                                      (Ω -           __________________________________________________________________________                                                             cm)                  101  900   Ag   Air   30   120  300 150  5.0  40    2200 >10.sup.13           102  900   Ag   Air   30   120  300 150  4.9  41    2300 >10.sup.13           103  910   Ag--Pd                                                                             Air   30   120  300 150  4.8  43    2300 >10.sup.13           104  880   Cu   N.sub.2                                                                             30   120  250 120  5.1  40    2200 >10.sup.13           105  850   Cu   N.sub.2                                                                             30   120  250 120  5.5  43    2300 >10.sup.13           106  850   Cu   N.sub.2                                                                             30   120  250 120  4.7  46    2600 >10.sup.13           107  900   Cu   N.sub.2 + H.sub.2                                                                   40   150  300 150  5.4  40    2300 >10.sup.13           108  910   Cu   N.sub.2 + H.sub.2                                                                   40   150  300 150  5.2  44    2300 >10.sup.13           109  900   Ag   Air   40   150  300 150  4.9  48    2400 >10.sup.13           110  900   Ag   Air   40   150  300 150  4.6  49    2600 >10.sup.13           111  890   Ag   Air   40   150  300 200  5.4  43    2700 >10.sup.13           112  880   Ag   Air   40   150  300 200  5.2  47    2500 >10.sup.13           113  900   Ag--Pd                                                                             Air   40   150  300 200  5.1  49    2400 >10.sup.13           114  880   Ag--Pd                                                                             Air   30   150  300 200  4.8  52    2600 >10.sup.13           115  880   Ag--Pd                                                                             Air   30   100  200 100  6.1  41    2600 >10.sup.13           116  900   Ag--Pd                                                                             Air   30   100  200 100  5.8  45    2400 >10.sup.13           117  870   Ag   Air   30   100  250 120  5.8  46    2500 >10.sup.13           118  850   Ag   Air   30   100  250 120  5.6  49    2500 >10.sup.13           119  890   Ag   Air   30   100  250 120  5.8  47    2700 >10.sup.13           120  900   Ag   Air   35   100  300 150  5.7  47    2500 >10.sup.13           __________________________________________________________________________

                                      TABLE 6                                     __________________________________________________________________________                          Number                                                                             Size of Wire       Coefficient                          Sintering        of   Wire Wire                                                                              Via  Specific                                                                           of Thermal                                                                          Breaking                                                                           Insulation           Sample                                                                             Temperature                                                                              Sintering                                                                           Layers                                                                             Width                                                                              Pitch                                                                             Diameter                                                                           Inductive                                                                          Expansion                                                                           Strength                                                                           Resistance           No   (°C.)                                                                        Conductor                                                                          Atmosphere                                                                          (Layer)                                                                            (μm)                                                                            (μm)                                                                           (μm)                                                                            Capacity                                                                           (×10.sup.-7 deg.sup.-1                                                  )     (kg/cm.sup.2)                                                                      (Ω -           __________________________________________________________________________                                                             cm)                  121  900   Cu   N.sub.2                                                                             35   100  300 150  5.7  43    2500 >10.sup.13           122  850   Cu   N.sub.2                                                                             35   100  300 150  5.4  48    2800 >10.sup.13           123  930   Cu   N.sub.2                                                                             35   100  300 150  6.4  39    2400 >10.sup.13           124  900   Cu   N.sub.2                                                                             40   150  300 150  5.7  45    2500 >10.sup.13           125  910   Cu   N.sub.2 + H.sub.2                                                                   40   150  350 150  5.5  48    2500 >10.sup.13           126  900   Au   Air   40   150  350 150  5.4  50    2600 >10.sup.13           127  900   Ag   Air   40   150  250 150  5.4  51    2700 >10.sup.13           128  880   Cu   N.sub.2                                                                             40   150  250 150  5.8  53    2800 >10.sup.13           129  950   Cu   N.sub.2                                                                             40   120  300 120  6.3  45    2500 >10.sup.13           130  930   Ag--Pd                                                                             Air   30   120  300 120  6.2  47    2500 >10.sup.13           131  900   Ag--Pd                                                                             Air   30   120  300 120  6.0  49    2400 >10.sup.13           132  900   Au   Air   30   120  300 120  5.8  51    2300 >10.sup.13           133  930   Cu   N.sub.2                                                                             30   120  250 100  6.3  48    2400 >10.sup.13           134  910   Cu   N.sub.2                                                                             30   120  250 100  6.1  50    2400 >10.sup.13           135  950   Ag--Pd                                                                             Air   30   120  250 100  6.0  51    2300 >10.sup.13           136  950   Ag--Pd                                                                             Air   30   100  200  80  6.0  51    2300 >10.sup.13           137  930   Ag--Pd                                                                             Air   40   100  250 120  6.3  50    2400 >10.sup.13           138  960   Ag--Pd                                                                             Air   40   100  250 120  6.1  52    2300 >10.sup.13           139  900   Ag   Air   40   100  250 120  6.0  54    2200 >10.sup.13           140  900   Cu   N.sub.2                                                                             40    80  200  80  6.1  55    2100 >10.sup.13           __________________________________________________________________________

When the content of silica glass powder is less than 10 wt %, thedielectric constant become higher than 7. On the other hand, if thecontent of silica glass powder exceed 30 wt %, satisfactory sinteringcan not be carried out so that the insulation resistance becomes lowerand the bending strength become lower than 2,000 kg/cm².

When the particle size of alumina powder used becomes lower than 0.5 μmor higher than 3 μm, the particle size of borosilicate magnesium glasspowder become lower than 1 μm or higher than 5 μm and the particle sizeof silica glass powder become lower than 0.5 μm or higher than 10 μm,the mixed material powder can not be sintered satisfactorily, so thatthe resulting multilayer glass ceramic substrate shows very poorreliability and hence can not be used in practical uses.

By the same reason as Example 1, practical multilayer glass ceramicsubstrate can not be obtained outside the proportions according to thepresent invention (12 to 59.6 wt % of alumina, 18 to 69.6 wt % ofborosilicate magnesium glass and higher than 1 wt % of cordieritecrystal).

By the same reason as Example 1, if the content of magnesium in theborosilicate magnesium glass used becomes less than 5 wt % in term ofmagnesium oxide, no or little cordierite crystal is produced bysintering operation.

EXAMPLE 3

(Alumina+borosilicate magnesium glass+mullite)

Example 2 is repeated except silica glass was replaced by mullitepowder.

Namely, alumina powder, borosilicate magnesium glass powder and mullitepowder having the average particle size of 0.5 μm to 10 μm wereintimately mixed at a proportion) of (alumina+mullite): borosilicatemagnesium glass of from 30 wt %:70 wt % to 60 wt %:40 wt %. Theproportion of alumina powder was adjusted above 10 wt %.

Composition of glass ceramic layer of sintered substrates obtained aresummarized in Table 7 and conductor, sintering conditions, numbers oflayers and wiring specification used for manufacturing multilayer glassceramic substrates as well as the results obtained are summarized inTables 8 and 9. The sample numbers in Table 7 correspond to those inTables 8 and 9.

                  TABLE 7                                                         ______________________________________                                        Alumina + borosilicate magnesium glass + mullite                              Composition ratio (wt %)                                                      Sample                     Borosilicate type                                                                       Cordierite                               Number  Alumina  Mullite   Glass     crystal                                  ______________________________________                                        201     12.0     21.0      37.0      30.0                                     202     12.0     30.0      33.0      25.0                                     203     12.4     11.0      69.6      20.0                                     204     17.0     25.0      32.0      26.0                                     205     17.0     10.0      23.0      50.0                                     206     18.0     21.0      40.0      21.0                                     207     22.0     18.0      25.0      35.0                                     208     23.0     15.0      27.0      35.0                                     209     23.0     19.0      38.0      20.0                                     210     23.0     24.0      20.0      33.0                                     211     28.0     20.0      19.0      33.0                                     212     28.0     11.0      51.0      10.0                                     213     28.0     17.0      40.0      15.0                                     214     28.0     17.0      35.0      20.0                                     215     33.0     17.0      36.0      14.0                                     216     33.0     12.0      25.0      30.0                                     217     33.0     18.0      20.0      29.0                                     218     34.0     10.0      45.0      11.0                                     219     38.0     19.0      18.0      25.0                                     220     38.0     24.0      24.0      14.0                                     221     39.0     15.0      28.0      18.0                                     222     39.0     11.0      40.0      10.0                                     223     42.0     11.0      18.0      29.0                                     224     42.0     12.0      28.0      18.0                                     225     42.0     10.0      30.0      18.0                                     226     42.5     13.0      34.5      10.0                                     227     46.0     10.0      31.0      23.0                                     228     46.0     11.0      33.0      10.0                                     229     48.0     11.0      18.0      23.0                                     230     48.0     12.0      21.0      19.0                                     231     49.0     10.0      21.0      20.0                                     232     49.0     15.0      26.0      10.0                                     233     52.0     12.0      18.0      18.0                                     234     52.0     12.0      20.0      16.0                                     235     53.0     11.0      22.0      14.0                                     236     53.0     11.0      24.0      12.0                                     237     56.0     10.0      25.0      9.0                                      238     56.0     10.0      21.0      13.0                                     239     57.0     10.0      24.0      9.0                                      240     59.6     10.0      19.4      11.0                                     ______________________________________                                    

                                      TABLE 8                                     __________________________________________________________________________                          Number                                                                             Size of Wire       Coefficient                          Sintering        of   Wire Wire                                                                              Via  Specific                                                                           of Thermal                                                                          Breaking                                                                           Insulation           Sample                                                                             Temperature                                                                              Sintering                                                                           Layers                                                                             Width                                                                              Pitch                                                                             Diameter                                                                           Inductive                                                                          Expansion                                                                           Strength                                                                           Resistance           No   (°C.)                                                                        Conductor                                                                          Atmosphere                                                                          (Layer)                                                                            (μm)                                                                            (μm)                                                                           (μm)                                                                            Capacity                                                                           (×10.sup.-7 deg.sup.-1                                                  )     (kg/cm.sup.2)                                                                      (Ω -           __________________________________________________________________________                                                             cm)                  201  900   Ag   Air   30   120  300 150  5.4  40    2200 >10.sup.13           202  900   Ag   Air   30   120  300 150  5.3  41    2300 >10.sup.13           203  910   Ag--Pd                                                                             Air   30   120  300 150  5.2  43    2300 >10.sup.13           204  880   Cu   N.sub.2                                                                             30   120  250 120  5.5  40    2200 >10.sup.13           205  850   Cu   N.sub.2                                                                             30   120  250 120  5.5  43    2300 >10.sup.13           206  850   Cu   N.sub.2                                                                             30   120  250 120  5.1  46    2600 >10.sup.13           207  900   Cu   N.sub.2 + H.sub.2                                                                   40   150  300 150  5.8  40    2300 >10.sup.13           208  910   Cu   N.sub.2 + H.sub.2                                                                   40   150  300 150  5.6  44    2300 >10.sup.13           209  900   Ag   Air   40   150  300 150  5.3  48    2400 >10.sup.13           210  900   Ag   Air   40   150  300 150  5.0  49    2600 >10.sup.13           211  890   Ag   Air   40   150  300 200  5.8  43    2700 >10.sup.13           212  880   Ag   Air   40   150  300 200  5.6  47    2500 >10.sup.13           213  900   Ag--Pd                                                                             Air   40   150  300 200  5.5  49    2400 >10.sup.13           214  880   Ag--Pd                                                                             Air   30   150  300 200  5.2  52    2600 >10.sup.13           215  880   Ag--Pd                                                                             Air   30   100  200 100  6.5  41    2600 >10.sup.13           216  900   Ag--Pd                                                                             Air   30   100  200 100  6.2  45    2400 >10.sup.13           217  870   Ag   Air   30   100  250 120  6.2  46    2500 >10.sup.13           218  850   Ag   Air   30   100  250 120  6.0  49    2500 >10.sup.13           219  890   Ag   Air   30   100  250 120  6.2  47    2700 >10.sup.13           220  900   Ag   Air   35   100  300 150  6.1  47    2500 >10.sup.13           __________________________________________________________________________

                                      TABLE 9                                     __________________________________________________________________________                          Number                                                                             Size of Wire       Coefficient                          Sintering        of   Wire Wire                                                                              Via  Specific                                                                           of Thermal                                                                          Breaking                                                                           Insulation           Sample                                                                             Temperature                                                                              Sintering                                                                           Layers                                                                             Width                                                                              Pitch                                                                             Diameter                                                                           Inductive                                                                          Expansion                                                                           Strength                                                                           Resistance           No   (°C.)                                                                        Conductor                                                                          Atmosphere                                                                          (Layer)                                                                            (μm)                                                                            (μm)                                                                           (μm)                                                                            Capacity                                                                           (×10.sup.-7 deg.sup.-1                                                  )     (kg/cm.sup.2)                                                                      (Ω -           __________________________________________________________________________                                                             cm)                  221  900   Cu   N.sub.2                                                                             35   100  300 150  6.1  43    2500 >10.sup.13           222  850   Cu   N.sub.2                                                                             35   100  300 150  5.8  48    2800 >10.sup.13           223  930   Cu   N.sub.2                                                                             35   100  300 150  6.8  39    2400 >10.sup.13           224  900   Cu   N.sub.2                                                                             40   150  300 150  6.1  45    2500 >10.sup.13           225  910   Cu   N.sub.2 + H.sub.2                                                                   40   150  350 150  5.9  48    2500 >10.sup.13           226  900   Au   Air   40   150  350 150  5.8  50    2600 >10.sup.13           227  900   Ag   Air   40   150  250 150  5.8  51    2700 >10.sup.13           228  880   Cu   N.sub.2                                                                             40   150  250 150  6.2  53    2800 >10.sup.13           229  950   Cu   N.sub.2                                                                             40   120  300 120  6.7  45    2500 >10.sup.13           230  930   Ag--Pd                                                                             Air   30   120  300 120  6.6  47    2500 >10.sup.13           231  900   Ag--Pd                                                                             Air   30   120  300 120  6.4  49    2400 >10.sup.13           232  900   Au   Air   30   120  300 120  6.2  51    2300 >10.sup.13           233  930   Cu   N.sub.2                                                                             30   120  250 100  6.7  48    2400 >10.sup.13           234  910   Cu   N.sub.2                                                                             30   120  250 100  6.5  50    2400 >10.sup.13           235  950   Ag--Pd                                                                             Air   30   120  250 100  6.4  51    2300 >10.sup.13           236  950   Ag--Pd                                                                             Air   30   100  200  80  6.4  51    2300 >10.sup.13           237  930   Ag--Pd                                                                             Air   40   100  250 120  6.7  50    2400 >10.sup.13           238  960   Ag--Pd                                                                             Air   40   100  250 120  6.5  52    2300 >10.sup.13           239  900   Ag   Air   40   100  250 120  6.4  54    2200 >10.sup.13           240  900   Cu   N.sub.2                                                                             40    80  200  80  6.5  55    2100 >10.sup.13           __________________________________________________________________________

When the content of mullite powder is less than 10 wt %, the dielectricconstant become higher than 7. On the other hand, if the content ofmullite powder exceed 30 wt %, satisfactory sintering can not be carriedout so that the insulation resistance becomes lower and the bendingstrength become lower than 2,000 kg/cm².

When the particle size of alumina powder used becomes lower than 0.5 μmor higher than 3 μm, the particle size of borosilicate magnesium glasspowder become lower than 1 μm or higher than 5 μm and the particle sizeof mullite powder become lower than 0.5 μm or higher than 10 μm, themixed material powder can not be sintered satisfactorily, so that theresulting multilayer glass ceramic, substrate shows very poorreliability and hence can not be used in practical uses.

By the same reason as Example 2, practical multilayer glass ceramicsubstrate can not be obtained outside the proportions according to thepresent invention (12 to 59.6 wt % of alumina, 18 to 69.6 wt % ofborosilicate magnesium glass and higher than 1 wt % of cordieritecrystal).

By the same reason as Example 2 if the cordierite of magnesium in theborosilicate magnesium glass used becomes less than 5 wt % in terms ofmagnesium oxide, no or little cordierite crystal is produced bysintering operation.

EXAMPLE 4

(Alumina+borosilicate magnesium glass+α-quartz)

Example 2 is repeated except silica glass was replaced by α-quartzpowder.

Namely, alumina powder, borosilicate (magnesium glass powder andα-quartz powder having the average particle size of 0.5 μm to 10 μm wereintimately mixed at a proportion of (alumina+α-quartz): borosilicatemagnesium glass of from 30 wt %:70 wt % to 60 wt %:40 wt %. Theproportion of alumina powder was adjusted above 10 wt %.

Composition of glass ceramic layer of sintered substrates obtained aresummarized in Table 10 and conductor, sintering conditions, numbers oflayers and wiring specification used for manufacturing multilayer glassceramic substrates as well as the results obtained are summarized inTables 11 and 12. The sample numbers Table 10 correspond to those inTables 11 and 12.

                  TABLE 10                                                        ______________________________________                                        quartza + borosilicate magnesium glass + α                              Composition ratio (wt %)                                                      Sample                     Borosilicate type                                                                       Cordierite                               Number  Alumina  α-quartz                                                                          Glass     crystal                                  ______________________________________                                        301     12.0     21.0      37.0      30.0                                     302     12.0     30.0      33.0      25.0                                     303     12.4     11.0      69.6      20.0                                     304     17.0     25.0      32.0      26.0                                     305     17.0     10.0      23.0      50.0                                     306     18.0     21.0      40.0      21.0                                     307     22.0     18.0      25.0      35.0                                     308     23.0     15.0      27.0      35.0                                     309     23.0     19.0      38.0      20.0                                     310     23.0     24.0      20.0      33.0                                     311     28.0     20.0      19.0      33.0                                     312     28.0     11.0      51.0      10.0                                     313     28.0     17.0      40.0      15.0                                     314     28.0     17.0      35.0      20.0                                     315     33.0     17.0      36.0      14.0                                     316     33.0     12.0      25.0      30.0                                     317     33.0     18.0      20.0      29.0                                     318     34.0     10.0      45.0      11.0                                     319     38.0     19.0      18.0      25.0                                     320     38.0     24.0      24.0      14.0                                     321     39.0     15.0      28.0      18.0                                     322     39.0     11.0      40.0      10.0                                     323     42.0     11.0      18.0      29.0                                     324     42.0     12.0      28.0      18.0                                     325     42.0     10.0      30.0      18.0                                     326     42.5     13.0      34.5      10.0                                     327     46.0     10.0      31.0      23.0                                     328     46.0     11.0      33.0      10.0                                     329     48.0     11.0      18.0      23.0                                     330     48.0     12.0      21.0      19.0                                     331     49.0     10.0      21.0      20.0                                     332     49.0     15.0      26.0      10.0                                     333     52.0     12.0      18.0      18.0                                     334     52.0     12.0      20.0      16.0                                     335     53.0     11.0      22.0      14.0                                     336     53.0     11.0      24.0      12.0                                     337     56.0     10.0      25.0      9.0                                      338     56.0     10.0      21.0      13.0                                     339     57.0     10.0      24.0      9.0                                      340     59.6     10.0      19.4      11.0                                     ______________________________________                                    

                                      TABLE 11                                    __________________________________________________________________________                          Number                                                                             Size of Wire       Coefficient                          Sintering        of   Wire Wire                                                                              Via  Specific                                                                           of Thermal                                                                          Breaking                                                                           Insulation           Sample                                                                             Temperature                                                                              Sintering                                                                           Layers                                                                             Width                                                                              Pitch                                                                             Diameter                                                                           Inductive                                                                          Expansion                                                                           Strength                                                                           Resistance           No   (°C.)                                                                        Conductor                                                                          Atmosphere                                                                          (Layer)                                                                            (μm)                                                                            (μm)                                                                           (μm)                                                                            Capacity                                                                           (×10.sup.-7 deg.sup.-1                                                  )     (kg/cm.sup.2)                                                                      (Ω -           __________________________________________________________________________                                                             cm)                  301  900   Ag   Air   30   120  300 150  5.0  40    2200 >10.sup.13           302  900   Ag   Air   30   120  300 150  4.9  41    2300 >10.sup.13           303  910   Ag--Pd                                                                             Air   30   120  300 150  4.8  43    2300 >10.sup.13           304  880   Cu   N.sub.2                                                                             30   120  250 120  5.1  40    2200 >10.sup.13           305  850   Cu   N.sub.2                                                                             30   120  250 120  5.5  43    2300 >10.sup.13           306  850   Cu   N.sub.2                                                                             30   120  250 120  4.7  46    2600 >10.sup.13           307  900   Cu   N.sub.2 + H.sub.2                                                                   40   150  300 150  5.4  40    2300 >10.sup.13           308  910   Cu   N.sub.2 + H.sub.2                                                                   40   150  300 150  5.2  44    2300 >10.sup.13           309  900   Ag   Air   40   150  300 150  4.9  48    2400 >10.sup.13           310  900   Ag   Air   40   150  300 150  4.6  49    2600 >10.sup.13           311  890   Ag   Air   40   150  300 200  5.4  43    2700 >10.sup.13           312  880   Ag   Air   40   150  300 200  5.2  47    2500 >10.sup.13           313  900   Ag--Pd                                                                             Air   40   150  300 200  5.1  49    2400 >10.sup.13           314  880   Ag--Pd                                                                             Air   30   150  300 200  4.8  52    2600 >10.sup.13           315  880   Ag--Pd                                                                             Air   30   100  200 100  6.1  41    2600 >10.sup.13           316  900   Ag--Pd                                                                             Air   30   100  200 100  5.8  45    2400 >10.sup.13           317  870   Ag   Air   30   100  250 120  5.8  46    2500 >10.sup.13           318  850   Ag   Air   30   100  250 120  5.6  49    2500 >10.sup.13           319  890   Ag   Air   30   100  250 120  5.8  47    2700 >10.sup.13           320  900   Ag   Air   35   100  300 150  5.7  47    2500 >10.sup.13           __________________________________________________________________________

                                      TABLE 12                                    __________________________________________________________________________                          Number                                                                             Size of Wire       Coefficient                          Sintering        of   Wire Wire                                                                              Via  Specific                                                                           of Thermal                                                                          Breaking                                                                           Insulation           Sample                                                                             Temperature                                                                              Sintering                                                                           Layers                                                                             Width                                                                              Pitch                                                                             Diameter                                                                           Inductive                                                                          Expansion                                                                           Strength                                                                           Resistance           No   (°C.)                                                                        Conductor                                                                          Atmosphere                                                                          (Layer)                                                                            (μm)                                                                            (μm)                                                                           (μm)                                                                            Capacity                                                                           (×10.sup.-7 deg.sup.-1                                                  )     (kg/cm.sup.2)                                                                      (Ω -           __________________________________________________________________________                                                             cm)                  321  900   Cu   N.sub.2                                                                             35   100  300 150  5.7  43    2500 >10.sup.13           322  850   Cu   N.sub.2                                                                             35   100  300 150  5.4  48    2800 >10.sup.13           323  930   Cu   N.sub.2                                                                             35   100  300 150  6.4  39    2400 >10.sup.13           324  900   Cu   N.sub.2                                                                             40   150  300 150  5.7  45    2500 >10.sup.13           325  910   Cu   N.sub.2 + H.sub.2                                                                   40   150  350 150  5.5  48    2500 >10.sup.13           326  900   Au   Air   40   150  350 150  5.4  50    2600 >10.sup.13           327  900   Ag   Air   40   150  250 150  5.4  51    2700 >10.sup.13           328  880   Cu   N.sub.2                                                                             40   150  250 150  5.8  53    2800 >10.sup.13           329  950   Cu   N.sub.2                                                                             40   120  300 120  6.3  45    2500 >10.sup.13           330  930   Ag--Pd                                                                             Air   30   120  300 120  6.2  47    2500 >10.sup.13           331  900   Ag--Pd                                                                             Air   30   120  300 120  6.0  49    2400 >10.sup.13           332  900   Au   Air   30   120  300 120  5.8  51    2300 >10.sup.13           333  930   Cu   N.sub.2                                                                             30   120  250 100  6.3  48    2400 >10.sup.13           334  910   Cu   N.sub.2                                                                             30   120  250 100  6.1  50    2400 >10.sup.13           335  950   Ag--Pd                                                                             Air   30   120  250 100  6.0  51    2300 >10.sup.13           336  950   Ag--Pd                                                                             Air   30   100  200  80  6.0  51    2300 >10.sup.13           337  930   Ag--Pd                                                                             Air   40   100  250 120  6.3  50    2400 >10.sup.13           338  960   Ag--Pd                                                                             Air   40   100  250 120  6.1  52    2300 >10.sup.13           339  900   Ag   Air   40   100  250 120  6.0  54    2200 >10.sup.13           340  900   Cu   N.sub.2                                                                             40    80  200  80  6.1  55    2100 >10.sup.13           __________________________________________________________________________

When the content of α-quartz powder is less than 10 wt %, the dielectricconstant become higher than 7. On the other hand, if the content ofa-quartz powder exceed 30 wt %, satisfactory sintering can not becarried out so that the insulation resistance becomes lower and thebending strength become lower than 2,000 kg/cm².

When the particle size of alumina powder used becomes lower than 0.5 μmor higher than 3 μm, the particle size of borosilicate magnesium glasspowder become lower than 1 μm or higher than 5 μm and the particle sizeof α-quartz powder become lower than 0.5 μm or higher than 10 μm, themixed material powder can not be sintered satisfactorily, so that theresulting multilayer glass ceramic substrate shows very poor reliabilityand hence can not be used in practical uses.

By the same reason as Example 2, practical multilayer glass ceramicsubstrate can not be obtained outside the proportions according to thepresent invention (12 to 59.6 wt % of alumina, 18 to 69.6 wt % ofborosilicate magnesium glass and higher than 1 wt % of cordieritecrystal).

By the same reason as Example 2, if the, contents of magnesium in theborosilicate magnesium glass used becomes less than 5 wt % in term ofmagnesium oxide, no or little cordierite crystal is produced bysintering operation.

We claim:
 1. A multilayer glass ceramic substrate having a plurality ofconductor layers, each of said conductor layers being laminated througha glass ceramic layer, said glass ceramic layer having a compositioncomprising alumina, borosilicate magnesium glass, and cordierite crystalproduced by chemical reaction between said alumina and said borosilicatemagnesium glass; said cordierite being chemically bonded with both saidalumina and said borosilicate magnesium glass during sintering, thecontent of said composition being about 12 to 59.6 wt % alumina, about18 to 69.6 wt % borosilicate magnesium glass, and about 1 to 50 wt %cordierite crystal, the sum of components in said composition being 100wt %, said substrate having a bending strength of at least 2,000 kg/cm².2. The substrate of claim 1 further comprising said glass ceramic layerhaving as essential ingredients based on the weight of the essentialingredients 12-59.6 wt % alumina; 18-69.6 wt % borosilicate magnesium;and 1-50 wt % cordierite crystal.
 3. A multilayer glass ceramicsubstrate having a plurality of conductor layers each laminated througha glass ceramic layer, characterized in that said glass ceramic layerhas a composition comprising alumina, borosilicate magnesium glass andcordierite crystal produced by chemical reaction between said aluminaand borosilicate magnesium glass caused by sintering, the content ofsaid alumina being substantially 12 to 59.6% wt %, the content of saidborosilicate magnesium glass being substantially 18 to 69.6% wt %, andthe content of the cordierite crystal being substantially 1 to 50 wt %,said composition further containing a fourth component selected from thegroup consisting of silica glass, α-quartz and mullite, the content ofsaid fourth component being 10 to 30 wt %, the sum of said componentsbeing 100 wt %, said substrate having a bending strength of at least2,000 kg/cm².